Automatic identification (“Auto-ID”) technology is used to help machines identify objects and capture data automatically. One of the earliest Auto-ID technologies was the bar code, which uses an alternating series of thin and wide bands that can be digitally interpreted by an optical scanner. This technology gained widespread adoption and near-universal acceptance with the designation of the Universal Product Code (“UPC”)—a standard governed by an industry-wide consortium called the Uniform Code Council. Formally adopted in 1973, the UPC is one of the most ubiquitous symbols present on virtually all manufactured goods today and has allowed for enormous efficiency in the tracking of goods through the manufacturing, supply, and distribution of various goods.
However, the bar code still requires manual interrogation by a human operator to scan each tagged object individually with a scanner. This is a line-of-sight process that has inherent limitations in speed and reliability. In addition, the UPC bar codes only allow for manufacturer and product type information to be encoded into the barcode, not the unique item's serial number. The bar code on one milk carton is the same as every other, making it impossible to count objects or individually check expiration dates, much less find one particular carton of many.
Currently, retail items are marked with barcode labels. These printed labels have over 40 “standard” layouts, can be mis-printed, smeared, mis-positioned and mis-labeled. In transit, these outer labels are often damaged or lost. Upon receipt, the pallets typically have to be broken-down and each case scanned into an enterprise system. Error rates at each point in the supply chain have been 4-18% thus creating a billion dollar inventory visibility problem. However, Radio Frequency Identification (RFID) allows the physical layer of actual goods to automatically be tied into software applications, to provide accurate tracking.
The emerging RFID technology employs a Radio Frequency (RF) wireless link and ultra-small embedded computer chips, to overcome these barcode limitations. RFID technology allows physical objects to be identified and tracked via these wireless “tags”. It functions like a bar code that communicates to the reader automatically without needing manual line-of-sight scanning or singulation of the objects.
In the design of RF antennas, it is often desirable to achieve an antenna gain pattern that is independent of orientation in any direction, i.e., fully spherical in all three dimensions. Most single antenna designs suffer from attenuation in at least one direction. This usually results in greater difficulties during installations and reduced reliability over changing environmental conditions. Some solutions have included using multiple antenna and transceiver hardware systems to more completely cover all orientations of the desired signals. Such RFID tags usually have two antenna ports, with one antenna per port. This configuration is used for polarization. However, if the tag is lying flat on a table, both antennas become detuned, and the tag may lose the ability to communicate.
Therefore, it would be desirable to create an RF design that exhibits good gain characteristics while maintaining a fully omni directional (isotropic) pattern in free space, and which further does not become detuned when placed against a metal or dielectric surface.
In conjunction with the desire for orientation-independent functionality, it is also desirable to miniaturize the entire transceiver. However, miniaturization urges physical positioning of all of the electronic components near the antenna. The location of conducting elements within the field of the antenna has heretofore generally resulted in the antenna's characteristics being modified, usually in an undesirable fashion. This has been dealt with previously by simply accepting the degraded performance, or by physically separating the antenna from other conductive elements, resulting in an undesirably larger size.
What is therefore needed is a way to reduce physical size of the RF device while maintaining optimal antenna characteristics.